Traditionally urea-derived products such as liquid compositions comprising DHEU, for example aqueous compositions, were produced by reacting solid urea with a solution of glyoxal to form a liquid composition comprising DHEU. The resulting liquid composition comprising DHEU also contained unreacted urea and/or urea derivatives and/or unreacted glyoxal and/or glyoxal derivatives and glycoluril, a byproduct of urea, for example excess urea, reacting with DHEU and/or glycoluril derivatives. These known liquid compositions comprising DHEU contained significant amounts of glycoluril, which is an undesired byproduct of the reaction for certain uses of the liquid composition, for example when it is used as a crosslinking agent in the formation of a hydroxyl polymer filament. The known liquid compositions described above contained much greater than 4000 ppm, for example 5000-6000 ppm, of glycoluril including any glycoluril derivatives and/or much greater than 2% on weight of DHEU of glycoluril including any glycoluril derivatives.
One approach that formulators have taken to reduce the level of glycoluril including glycoluril derivatives in the liquid compositions comprising DHEU is to crystallize the DHEU. The crystallization of the DHEU from the liquid composition comprising the DHEU, urea, and glycoluril including any glycoluril derivatives results in a pure solid DHEU. This pure solid DHEU may then be dissolved to form a liquid composition comprising DHEU and no or no detectable level of glycoluril nor glycoluril derivatives, and no or no detectable level of urea nor urea derivatives (thus glycoluril including glycoluril derivatives and urea and urea derivatives have been eliminated from this liquid composition comprising DHEU). However, the crystallization/purification process has its negatives, for example it is difficult to obtain yields of greater than 50% by weight of DHEU from the original reactants. One problem faced by formulators of liquid compositions comprising DHEU is how to produce a liquid composition comprising DHEU, with or without urea, and with less glycoluril including glycoluril derivatives than known liquid compositions comprising DHEU with minimal steps, for example without crystallizing and/or purifying the DHEU from the other components in the liquid composition comprising DHEU and/or without significant yield loss of the DHEU.
Accordingly, there is a need for liquid compositions comprising DHEU, with or without urea and/or urea derivatives, and minimal (less than 4000 ppm and/or less than 2% on weight of DHEU) to no or no-detectable level glycoluril including glycoluril derivatives and methods for making such liquid compositions.